Do not automatically inject bounds (#879)

Fixes #878

Author: maurer

zeroize/derive/src/lib.rs

@@ -8,11 +8,10 @@ use proc_macro2::{Ident, TokenStream};
 use quote::{format_ident, quote};
 use syn::{
     parse::{Parse, ParseStream},
-    parse_quote,
     punctuated::Punctuated,
     token::Comma,
-    Attribute, Data, DeriveInput, Expr, ExprLit, Field, Fields, GenericParam, Lit, Meta, Result,
-    Variant, WherePredicate,
+    Attribute, Data, DeriveInput, Expr, ExprLit, Field, Fields, Lit, Meta, Result, Variant,
+    WherePredicate,
 };
 
 /// Name of zeroize-related attributes
@@ -39,16 +38,7 @@ fn derive_zeroize_impl(input: DeriveInput) -> TokenStream {
 
     let extra_bounds = match attributes.bound {
         Some(bounds) => bounds.0,
-        None => {
-            let mut out: Punctuated<WherePredicate, Comma> = Default::default();
-            for param in &input.generics.params {
-                if let GenericParam::Type(type_param) = param {
-                    let type_name = &type_param.ident;
-                    out.push(parse_quote! { #type_name: Zeroize })
-                }
-            }
-            out
-        }
+        None => Default::default(),
     };
 
     let mut generics = input.generics.clone();

zeroize/tests/zeroize_derive.rs

@@ -325,3 +325,29 @@ fn derive_zeroize_on_drop_generic() {
     #[derive(ZeroizeOnDrop)]
     struct Z<T: Zeroize>(Vec<T>);
 }
+
+#[test]
+fn derive_zeroize_unused_param() {
+    #[derive(Zeroize)]
+    struct Z<T> {
+        arr: [u32; 5],
+        #[zeroize(skip)]
+        skipped: T,
+    }
+}
+
+#[test]
+// Issue #878
+fn derive_zeroize_with_marker() {
+    #[derive(ZeroizeOnDrop, Zeroize)]
+    struct Test<A: Marker> {
+        #[zeroize(skip)]
+        field: Option<A>,
+    }
+
+    trait Secret: ZeroizeOnDrop + Zeroize {}
+
+    impl<A: Marker> Secret for Test<A> {}
+
+    trait Marker {}
+}